One problem you're likely to run into is discovering what the curve is for the temperature response of the thermistor. You have to know its resistance response to a change in temperature in order to make sense of what you input to the PLC. That relationship between the resistance and temperature, as mentioned previously, is not linear.
But maybe you'll figure that out.
Us old farts think alike. I echo BobB's sentiments, and would recommend using a thermocouple or RTD. But if you can't substitute a thermocouple or an RTD, and really need to use that thermistor, then you'll need an analog input card for your PLC that can read resistance over the range of your thermistor. No, none of us can tell you what the range is for your thermistor. There's no 'standard'. You can put an ohmmeter across it and see what resistance it has at whatever temperature it's at.
I suspect that the thermistor resistance is high enough that the resistance of the copper wire used for connecting is not a factor (unlike 100 ohm platinum 2 wire RTD's where it is a factor)
Or, if you can find a constant current source you could pump current through the thermistor and read the voltage drop across the thermistor with a dc voltage analog input card.
Or you can try to find a transmitter to convert to a conventional 4-20mA signal that is might or might not be linearized, which would require a 4-20mA analog input card for your PLC.
Cole Parmer sells a 'thermistor' transmitter, but check out the caveats:
"
Thermistor Transmitter is compatible with 400 series thermistor probes for excellent accuracy over the ambient temperature range."
http://www.coleparmer.com/catalog/product_view.asp?sku=9477110&pfx=
Here's another thermisotor to 4-20ma transmitter, but be warned that it's for specific thermistor curves.
http://www.robertoweninc.com/produc...ng/4-20ma/resistance/thermistor/hardware.html